/*
 *
 * A JavaScript implementation of the Secure Hash Algorithm, SHA-1, as defined
 * in FIPS PUB 180-1
 *
 * By lizq
 *
 * 2006-11-11
 *
 */
/*
 *
 * Configurable variables.
 *
 */
const hexcase = 0; /* hex output format. 0 - lowercase; 1 - uppercase */
const chrsz = 8; /* bits per input character. 8 - ASCII; 16 - Unicode */
/*
 *
 * The main function to calculate message digest
 *
 */
export default function hex_sha1(s) {
  return binb2hex(core_sha1(AlignSHA1(s)));
}

/*
 *
 * Perform a simple self-test to see if the VM is working
 *
 */
function sha1_vm_test() {
  return hex_sha1('abc') == 'a9993e364706816aba3e25717850c26c9cd0d89d';
}

/*
 *
 * Calculate the SHA-1 of an array of big-endian words, and a bit length
 *
 */
function core_sha1(blockArray) {
  const x = blockArray; // append padding
  const w = Array(80);

  let a = 1732584193;

  let b = -271733879;

  let c = -1732584194;

  let d = 271733878;

  let e = -1009589776;

  for (
    let i = 0;
    i < x.length;
    i += 16 // 每次处理512位 16*32
  ) {
    const olda = a;

    const oldb = b;

    const oldc = c;

    const oldd = d;

    const olde = e;

    for (
      let j = 0;
      j < 80;
      j++ // 对每个512位进行80步操作
    ) {
      if (j < 16) w[j] = x[i + j];
      else w[j] = rol(w[j - 3] ^ w[j - 8] ^ w[j - 14] ^ w[j - 16], 1);

      const t = safe_add(
        safe_add(rol(a, 5), sha1_ft(j, b, c, d)),
        safe_add(safe_add(e, w[j]), sha1_kt(j))
      );

      e = d;

      d = c;

      c = rol(b, 30);

      b = a;

      a = t;
    }

    a = safe_add(a, olda);

    b = safe_add(b, oldb);

    c = safe_add(c, oldc);

    d = safe_add(d, oldd);

    e = safe_add(e, olde);
  }

  return new Array(a, b, c, d, e);
}

/*
 *
 * Perform the appropriate triplet combination function for the current
 * iteration
 *
 * 返回对应F函数的值
 *
 */
function sha1_ft(t, b, c, d) {
  if (t < 20) return (b & c) | (~b & d);

  if (t < 40) return b ^ c ^ d;

  if (t < 60) return (b & c) | (b & d) | (c & d);

  return b ^ c ^ d; // t<80
}

/*
 *
 * Determine the appropriate additive constant for the current iteration
 *
 * 返回对应的Kt值
 *
 */
function sha1_kt(t) {
  return t < 20 ? 1518500249 : t < 40 ? 1859775393 : t < 60 ? -1894007588 : -899497514;
}

/*
 *
 * Add integers, wrapping at 2^32. This uses 16-bit operations internally
 *
 * to work around bugs in some JS interpreters.
 *
 * 将32位数拆成高16位和低16位分别进行相加，从而实现 MOD 2^32 的加法
 *
 */
function safe_add(x, y) {
  const lsw = (x & 0xffff) + (y & 0xffff);

  const msw = (x >> 16) + (y >> 16) + (lsw >> 16);

  return (msw << 16) | (lsw & 0xffff);
}

/*
 *
 * Bitwise rotate a 32-bit number to the left.
 *
 * 32位二进制数循环左移
 *
 */
function rol(num, cnt) {
  return (num << cnt) | (num >>> (32 - cnt));
}

/*
 *
 * The standard SHA1 needs the input string to fit into a block
 *
 * This function align the input string to meet the requirement
 *
 */
function AlignSHA1(str) {
  const nblk = ((str.length + 8) >> 6) + 1;

  const blks = new Array(nblk * 16);

  for (var i = 0; i < nblk * 16; i++) blks[i] = 0;

  for (i = 0; i < str.length; i++) blks[i >> 2] |= str.charCodeAt(i) << (24 - (i & 3) * 8);

  blks[i >> 2] |= 0x80 << (24 - (i & 3) * 8);

  blks[nblk * 16 - 1] = str.length * 8;

  return blks;
}

/*
 *
 * Convert an array of big-endian words to a hex string.
 *
 */
function binb2hex(binarray) {
  const hex_tab = hexcase ? '0123456789ABCDEF' : '0123456789abcdef';

  let str = '';

  for (let i = 0; i < binarray.length * 4; i++) {
    str +=
      hex_tab.charAt((binarray[i >> 2] >> ((3 - (i % 4)) * 8 + 4)) & 0xf) +
      hex_tab.charAt((binarray[i >> 2] >> ((3 - (i % 4)) * 8)) & 0xf);
  }

  return str;
}

/*
 *
 * calculate MessageDigest accord to source message that inputted
 *
 */
function calcDigest() {
  const digestM = hex_sha1(document.SHAForm.SourceMessage.value);

  document.SHAForm.MessageDigest.value = digestM;
}
